Obstructive sleep apnea/hypopnea syndrome (OSAHS) is a well recognized disorder which may affect as much as 1-5% of the adult population. OSAHS is one of the most common causes of excessive daytime somnolence. OSAHS is most frequent in obese males, and it is the single most frequent reason for referral to sleep disorder clinics.
OSAHS is associated with conditions in which there is anatomic or functional narrowing of the patient's upper airway, and is characterized by an intermittent obstruction of the upper airway during sleep. The obstruction results in a spectrum of respiratory disturbances ranging from the total absence of airflow despite continued respiratory effort (apnea), to significant obstruction with or without reduced airflow (hypopnea, episodes of elevated upper airway resistance, and snoring). Morbidity associated with the syndrome arises from hypoxemia, hypercapnia, bradycardia and sleep disruption associated with the respiratory obstructions and arousals from sleep.
The pathophysiology of OSAHS is not fully worked out. However, it is now well recognized that obstruction of the upper airway during sleep is in part due to the collapsible behavior of the supraglottic segment of the respiratory airway during the negative intraluminal pressure generated by inspiratory effort. The human upper airway during sleep behaves substantially similar to a Starling resistor which by definition limits the flow to a fixed value irrespective of the driving (inspiratory) pressure. Partial or complete airway collapse can occur associated with the loss of airway tone, which is characteristic of the onset of sleep and may be exaggerated with OSAHS.
Since 1981, positive airway pressure (“PAP”) applied by a tightly fitted nasal mask worn during sleep has evolved to become the most effective treatment for this disorder, and is now the standard of care. The availability of this non-invasive form of therapy has resulted in extensive publicity for sleep apnea/hypopnea and increased appearance of large numbers of patients who previously may otherwise avoid medical treatment because of the fear of tracheostomy. Increasing the comfort of the system (e.g., by minimizing the applied nasal pressure) has been a major goal of research aimed at improving patient compliance with therapy.
PAP therapy has become the mainstay of treatment in Obstructive Sleep Disordered Breathing (“OSDB”), which includes Obstructive Sleep Apnea/Hypopnea, Upper Airway Resistance Syndrome, Snoring, exaggerated rises of sleep-induced collapsibility of the upper airway and all conditions in which inappropriate collapsing of a segment of the upper airway causes significant non-physiologic obstruction to airflow. Collapse of a portion of the airway generally occurs whenever pressure in the collapsible portion of the airway becomes sub-atmospheric. Stated another way, collapse occurs when pressure in the airway falls below a “tissue pressure” in the surrounding wall. PAP therapy is directed to maintaining pressure in the collapsible portion of the airway at or above the critical “tissue pressure” at all times. This goal is achieved by raising the airway pressure in the entire respiratory system to a level higher than this critical pressure.
Despite its success, conventional PAP systems have certain limitations. For example, the determination of the appropriate pressure for therapy, referred to as PAP titration, is normally performed in a sleep laboratory where a specific treatment pressure is determined. However, during the first week of treatment the necessary pressure to treat the OSDB may decrease, which results in a prescribed pressure that is too high and may compromise patient compliance. In addition, the patient may assume body positions or sleep stages, other than those occurring in the sleep laboratory that may change the therapeutic pressure. Finally, patients may require periodic retitration following changes in condition, such as weight gain or loss. Retitration of the PAP in the laboratory is usually expensive and is not part of the usual standard of care. Thus, there is a need for a system and method that would provide initial PAP titration and retitration to patients as required during subsequent treatments.